Walking out of the store, my wife mentioned that her bill seemed higher than estimated. We stopped and re-checked the receipt and sure enough the clerk missed about $19.00 in discount savings. We went back inside and the store promptly fixed the error.
We went to another store and made a few more purchases. An item rang-up at full price even though it was on sale, but the luckily clerk caught it.
Both transactions happened less than 20 minutes apart, which to me is statistically significant. I wonder how many other items I mistakenly paid full price for because I didn't think to re-check my receipt.
So if you are buying a lot of clearance stuff, or something just doesn't seem right make a point to stop and re-check your receipt.